cmake regex dependency check fails

[plafratt]

This line in the CXX_11_EXTENDED_REGEX_TEST throws an exception

std::regex rx(\"^(.*):([0-9]+):([0-9]+):?-:?([0-9]+):([0-9]+):?(@[A-Za-z,]+)?\", std::regex_constants::extended);

This causes the test program to return -1, which causes the cmake to fail. If I change the argument to an empty string, cmake passes and the rtags build works.

std::regex rx(\"\", std::regex_constants::extended);

I am just showing the test passing with the empty string just to show that doing this doesn't seem to cause any other problems.